In a patient with a large atrial myxoma, the phonocardiographic timing of the tumor plop has been correlated with the two-dimensional echocardiographic motion pattern of the cardiac mass. The tumor plop occurred at the time when the mass stopped its diastolic forward motion into the ventricle and made a strong impact on the interventricular septum and right ventricular posterior wall. Occurrence of tumor plop may require a large mass or long enough tumor stalk to allow the impact of the mass on the ventricular wall.